Former Mexican Mafia leader Ernest "Chuco" Castro spent 17 months working undercover for the FBI after he was arrested in late 1993 on weapons charges. He testified that he wore a hidden recording device at numerous Mexican Mafia meetings.

The prosecution also displayed several surveillance photographs of alleged Mexican Mafia gatherings attended by Castro.

In one photo, shot at Echo Park, Castro is shown meeting with representatives of the sprawling 18th Street gang and several rival gangs. The meeting was held so the Mexican Mafia--or La Eme, as it is commonly referred to on the streets--could mediate a dispute between 18th Street and its enemies, Castro testified.

The tapes played Thursday were often difficult to hear, with the participants drowned out by background noise or speaking in vague terms that Castro contends were used to confirm and order attacks against those who stood in the prison gang's way.

Castro offered his interpretation of the conversations over repeated objections by defense attorneys, who argued that his remarks were "improper testimony." The defense contends that the Mexican Mafia does not exist and has called Castro a provocateur.

Those remarks refer to a gang member Gallardo allegedly killed for not paying drug taxes to the Mexican Mafia, Castro testified.

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On another occasion, transcripts show Gallardo saying of several individuals:

"They gotta be dealt with."

the people were pretending to be Mexican Mafia members and had to be killed, according to Castro.

"If anyone was claiming to be an Eme member and wasn't," Castro said, "it warranted the death penalty."

Throughout the daylong testimony, several of the defendants stared coldly at Castro, who kept his eyes fixed straight ahead and spoke in a hushed, matter-of-fact tone.

Before the tapes were played, Castro discussed the killings of several victims, including Ana Lizarraga, a longtime Eastside anti-gang activist who worked as an advisor on Edward James Olmos' Mexican Mafia movie "American Me."

FBI officials have previously said she was slain, in part, because the gang perceived the film as disrespectful. She was gunned down in May 1992 by two masked assassins.

But in court Thursday, Castro offered another reason, saying Lizarraga was killed because she was a "rat" who had threatened to expose mafia drug dealing operations at the Ramona Gardens housing project on the Eastside.